Fluid operated drop hammer with valved piston

ABSTRACT

A drop hammer has an operating ram in which valve-controlled conduit means interconnect opposite ends of a cylinder of the ram to allow fluid to transfer between the ends of the cylinder.

United States Patent [15] 3,669,198 Elliott [4 1 June 13, 1972 [54] FLUID OPERATED DROP HAMMER WITH VALVED PISTON [56] References Cited [72] Inventor: Roger M. Elliott, Somersham, near Ip- UNITED STATES PATENTS swich, England 1,665,046 4/1928 Tucker ..l73/l27 [73] Asslgneez The British Steel Piling Company Limited, R1586 441877 Loomis Ipswich Sum! England 1,662,576 3/1928 Jeschke ..173/135 x [22] Filed: March 10, 1970 Primary Examiner-Emest R. Purser [21] Appl' 18339 Attorney.lones&Lockwood [30] Foreign Application Priority Data [57] ABSTRACT March 11, 1969 Great Britain ..12,814/69 A drop hammer has an operating am in which valvgqggntrolled conduit means interconnect opposite ends of a cylinder [52] US. Cl ..l73/l27, 91/224, 91/318 f the ram to allow fluid to transfer between the ends of the [51] Int. Cl ..E02d 7/10, F01] 21/04 li [58] Field ofSearch ..l73/l27, 134-138;

10 Claims, 6 Drawing Figures PATENTEDJUH 13 m2 SHEET 10F 4 PAIENTEDJun 1 3 m2 SHEET 30F 4 PATENTEDJUHBIBYZ 3,669,198

' SHEET nor 4 FLUID OPERATED DROP HAMMER WITH VALVED PISTON This invention relates to drop hammers in which a hammer weight is operated by at least one fluid pressure ram.

In such mechanisms, the impact forces that can be realized by the hammer weight are restricted because of the difficulty of bringing pressure fluid to the ram and taking exhaust fluid from the ram at a fast enough rate without encountering significant fluid friction forces that themselves limit the rate of flow. One previously proposed form of pile driver has hydraulic ram provided with inlet and outlet fluid accumulators close to its external connections so that, at least at that part of the ram operation cycle when a maximum hammer speed and a maximum fluid flow rate are required, a considerable part of the flow into and out of the ram need only pass between the ram and the accumulators.

- However, the provision of the accumulators makes the equipment more complicated and they are bulky and heavy items. Also problems are created in the design of the equipment because of the need to locate the accumulators so that the fluid flow paths between them and the ram are kept extremely short if they are to operate effectively.

According to the invention, there is provided a drop hammer including a fluid pressure operating mechanism comprising a ram having an upwardly extending cylinder and piston assembly, conduit means for interconnecting the spaces of the cylinder on opposite sides of the piston to permit a flow of fluid between said spaces, and valve means for said conduit means to isolate said cylinder spaces from each other, said valve means being displaceable by an increase of pressure within one of the cylinder spaces so as to shut off said flow whereby admission of pressure fluid to the other of said fluid spaces causes relative displacement between the cylinder and piston. Said conduit means may be disposed internally of the ram and pass through the piston.

Conveniently, a frame of the hammer has the ram cylinder secured to it by its upper end, the hammer weight being guided by the frame and being secured to a piston rod that projects downwardly from the cylinder and that is attached to said ram piston. Closure of the valve means in this arrange ment may be actuated by an increase in pressure in the cylinder space above the piston so that continuation of a pressure fluid flow to the space below the piston so that continuation of a pressure fluid flow to the space below the piston will then raise the piston and rod.

Preferably, the valve means comprises a displaceably mounted member arranged to be exposed at opposite sides to the fluid in said one space of the cylinder and to atmospheric pressure respectively. Resilient means may bias the member to a position in which the conduit means interconnects said cylinder spaces unless so displaced by a pressure increase in said space to a value substantially greater than atmospheric.

In a further preferred feature of the invention, the moving part of the ram is connected to the hammer weight by means permitting a limited relative displacement therebetween in the direction of ram movement and damping means are provided to reduce the relative speed between the piston and cylinder at the end of a downwards hammer stroke. Such means may comprise a receiving space to which the ram pressure fluid is supplied and an insertion element for said space, said element and space being associated with the ram piston and cylinder or parts movable with the piston and cylinder respectively, the element being arranged to enter said space during the final part of said downwards stroke, there being a restricted fluid exit from the space while its volume is being reduced by the entry of the element whereby an increased resistance is offered to relative movement between the piston and cylinder during the final part of the stroke.

One embodiment of the invention will be more particularly described with reference to the wherein:

FIG. 1 is a schematic illustration of a drop hammer according to the invention including its hydraulic circuit,

FIG. 2 is a detailed sectional view of the hydraulic ram of the hammer in FIG. 1,

accompanying drawings,

FIG. 3 is a schematic illustration of an alternative form of drop hammer according to the invention.

FIG. 4 is a schematic diagram of an automatic switching means for a drop hammer according; to the invention,

FIG. 5 is a side elevation, the left-hand half being shown in section, of a modified form of ram for the hammer of FIG. I, and

FIG. 6 is a similar side elevation illustrating a further modification of the ram of the hammer of FIG. 1.

Referring to FIGS. 1 and 2 of the drawings, the hammer comprises a frame 2 that can be mounted upon a pile (not shown) to be driven, a hammer weight 4 being vertically displaceable on guide means 24 of the frame by a hydraulic ram 6 that is attached at the upper end 8 of its cylinder 10 to the frame 2 and at the lower end 12 of its piston rod 14 to the hammer weight, the connection at 15 incorporating resilient shock-absorbing means, such as a rubber bushing. Respective fluid lines l6, 17 lead to connections l8, 19 respectively in the upper and lower ends of the cylinder at opposite sides of a piston 20 slidable in the cylinder and to which the upper end of the rod 14 is secured.

The piston 20 has a neck portion 22 threaded to the rod 14 and locked in position by a screw 241. Within the head of the piston a cylindrical bore 26 opens to the piston upper face and a passage 28 from the lower side of the head leads to an annular recess 30 in the bore wall. A cup-shaped spool 32 fits closely in the bore and is slidable from the position shown, by the action of the spring 34 compressed between the upper end of the rod 14 and a counterbore 36 in the underside of the spool, to bear against a circlip stop 38 at the upper end of the bore 26. When in this position an aperture 40 in the cylindrical wall of the spool is aligned with the recess 30 so that there is a through path for hydraulic fluid between the upper and lower cylinder spaces on opposite sides of the piston.

The piston rod has a hollow center 42 so that the space occupied by the spring 34, and hence the underside of the spool 32, is in direct communication with the exterior.

The operation of the ram can be described from the point at which the piston is at the bottom of the cylinder, when the hammer weight will be resting upon the pile dolly (not shown) and there is no hydraulic pressure in either of the lines l6, 17, the spool then being in its top or open position in the piston. By operation of a control valve 46, a hydraulic pump 44 supplies a pressure flow through line 17 to connection 19 of the cylinder. The fluid can flow freely through the piston to the upper part of the cylinder but a pressure relief valve 48 in the upper cylinder line 16 prevents return flow to receiver tank 52 until the pressure at the connection 18 has reached 100 psi.

As the pressure of the fluid in the cylinder increases, an unbalanced axial force develops on the spool 32 since only its upper side is exposed to the fluid and, at a fluid pressure of some 70 p.s.i., the force of the spring 34 and of friction acting on the pool is overcome. The spool therefore moves downwards and the upper and lower cylinder spaces are isolated from each other. Pressure fluid continues to enter the lower space so that the piston begins to rise in the cylinder bringing the hammer weight with it.

When the piston reaches the top of its stroke, the control valve 46 is switched so that the lower space is nowconnected to the tank 52 of the hydraulic circuit. The resulting pressure drop allows the piston and weight to fall. As the volume of the upper cylinder space increases, the pressure there dropsand the spool rises in its seating aging. Due to friction of the spool, this will occur when the upper space pressure is some 50 psi. The hydraulic fluid can then transfer between the upper and lower spaces and this has the function that any throttling effect that might be caused by return flow in the line 17 of fluid expelled from the lower space or by incoming flow in the line 16 of fluid to the upper space, is reduced so that there is less resistance to the fall of the weight.

Because of the presence of the rod 141 in the lower cylinder space, however, the upper space will require more fluid than that which is displaced from the lower space and to keep to a minimum the efi'ect this might have on the speed of fall of the weight, a non-return valve 54 is placed in parallel with the pressure relief valve 48 so that fluid can also bypass the valve 48 to be drawn into the upper cylinder space from the line 16. If desired, an enclosed tank 56 can be placed in the line 16 immediately beyond the non-return valve 54 and so provide a readily available source of fluid for this counterflow.

The cycle can be repeated, after the hammer weight has impacted the dolly, by switching the control valve 46 again. Alternatively, automatic switching means can be provided so that the cycle is self-repeating. Such means may comprise a port on the side of the cylinder, as indicated at 58, that will communicate with the lower cylinder space when the piston is in its top position, the pressure rise which occurs when the piston attains this position being relayed by control line 60 to operate the valve 46 and so connect the lower space again to the tank return. The switching of the valve 46 to raise the piston and weight can then be actuated by a trip 51 connected by the falling weight immediately before the end of its stroke.

Since the weight can be expected to attain a considerable speed in its descent, it is desirable to include means that will prevent or reduce the transmission of jarring forces to the ram itself and for this purpose there is provided means to damp the final descending motion of the piston. These means comprise a collar 62 on the neck of the piston and a smaller diameter sleeve 64 below it having a tapered lower end. At the bottom of the cylinder are complementary parts comprising a lower end bore 66 within which the sleeve 64 will slide closely, and a counterbore 68 that can be sealingly engaged by an O-ring 70 mounted on the collar 62. The fluid supply connection 19 is in communication with the cylinder lower space through the bore 66 and counterbore 68.

Thus, when the piston approaches the bottom of its stroke, the sleeve 64 begins to enter the bore 66 and the seal 70 reaches the wall of the counterbore 68. Fluid in the remaining free volume of the counterbore can then escape to the outlet 19 only through such a clearance as there is between the closely fitting sleeve 64 and wall 66 and through narrow passages 72, 74, 76 leading from the bottom of the counterbore 68, that are controlled by an adjustable restrictor plug 78. The retardation of the piston and piston rod is therefore applied in an increasing rate in the final part of the downward stroke rather than completely suddenly at the end of the stroke, but, because of the resilient connection between the rod and the hammer weight this has little effect on the speed of the weight at impact. So that this damping arrangement will not delay the raising of the piston when pressure fluid is subsequently applied to the connection 19, a bypass bore 80 is provided to give direct communication between the connection and the main space below the piston and the passages 72, 74, 76 do not therefore restrict the inflow of fluid.

The described embodiment may be modified in various ways. Thus, the spool 32 may be fixed to or form part of the piston, which would then have limited freedom of movement on the rod 14 to open and close the path between the cylinder spares. If it should be required to increase the rate of descent of the weight, springs may be provided to exert a downwards force on the weight, either directly or through its attached ram part, one possible arrangement of such springs being shown at 81 in FIG. 1: this may be required particularly when a construction according to the invention is to be employed for such work as rock-breaking where the ram is likely not to be mounted vertically. Also, it is possible to arrange the mechanism so that the hammer weight is raised and lowered by the ram cylinder while the piston rod remains fixed to the hammer frame. I

As an example of this last-mentioned modification, FIG. 3 shows a drop hammer in which piston 82 rests on a pile dolly (not shown) while its cylinder 84, which is integral with or is secured to the hammer weight, slides on the piston to impact the dolly. Parts similar to those described in the embodiment of FIGS. 1 and 2 are indicated by the same reference numbers and it will be noted that movement of the spool 32 against its spring 34 is now determined by a rise in pressure in the lower space of the cylinder. Fluid lines 16, 17 now connected to the cylinder lower and upper spaces respectively, may form part of an external hydraulic circuit similar to that shown in FIG. 1; the non-return valve 54 and tank 56 are now unnecessary, however, since the total internal volume of the upper and lower cylinder spaces remains substantially constant during operation.

To raise the weight, pressure fluid is supplied through the line 17 to the upper cylinder space so that when the spool 32 rises to isolate the upper and lower spaces from each other, the continuing flow of fluid from the line 17 raises the cylinder. In other respects, the arrangement may operate in the same manner as the first-described embodiment and similar damping means may be provided for the end of a working stroke, although these are not illustrated in FIG. 3.

An alternative form of automatic switching means is illustrated diagrammatically in FIG. 4. This comprises a solenoid 100, operating the valve 46 as in FIG. 1 to control the flow to the ram cylinder. A timer 102 having manual adjustment means incorporates in it an amplifier to provide a switching signal to the solenoid 100. On the drop hammer itself there is mounted an accelerometer arranged to function as an impact detector 104 to initiate a further cycle of movement. In operation, when the apparatus is first switched on, the solenoid 100 is energized so that the valve 46 admits hydraulic fluid to the ram cylinder to raise the hammer weight and the timer 102 is simultaneously set in operation. At the end of the period preset, the timer provides a signal to de-energize the valve so that the hammer weight drops. On impact of the weight at the end of its stroke, the impact detector 104 generates a signal that sets the timer 102 in operation again and re-energizes the valve solenoid 100 so that the cycle is repeated.

FIG. 5 shows a further modified cylinder and piston arrangement, similar in many respects to the construction illustrated in FIG. 1. It may be noted here, however, that the damping means provided are different from that earlier embodiment. The sleeve 64 now carries no collar and lower end bore 66 open into an upwardly widening counterbore 86. As the piston nears the lower end of the cylinder, therefore, the sleeve enters an increasingly restricted passage so that a progressive damping of the ram motion is generated. As in the first-described embodiment, the resilient connection between the piston rod and the hammer weight prevents this having any significant effect on the speed of the weight at impact. The inlet connection 19 opens into the counterbore 86 so that there is sufficient space between it and the sleeve 64 for the initial inlet flow when the weight is to be raised and no additional bypass connection is necessary.

It is also possible for the connection between the cylinder spaces to be made externally of the cylinder and piston, this being shown in FIG. 6 where a bypass valve arrangement is connected in a conduit 88 between the upper and lower fluid conduits 16, 17. The valve comprises a body 90 housing the valve spool 32 and its spring 34 similarly to the piston in the construction shown in FIG. 1. Passage 92 in the valve body has the aperture 40 of the spool 32 brought into register with it when the spring has forced the spool to its top position. Similarly again to the first-described embodiment, the underside of the spool is subject to atmospheric pressure, in this in stance by the provision of a side bore 94 in the valve body.

What I claim and desire to secure by Letters Patent is:

1. A drop hammer comprising, in combination, a carrier, a fluid pressure operating mechanism comprising a ram having a cylinder and piston assembly mounted on said carrier in an upwardly extending position, said piston dividing the cylinder interior into discrete spaces on opposite sides of the piston, conduit means arranged to interconnect said cylinder internal spaces, the conduit means being provided with valve means to isolate said spaces from each other, said valve means being displaceable by an increase of pressure in one of said spaces thereby causing a pressure force in that one space, which force displaces said valve means so as to shut off the flow between the spaces whereby admission of pressure fluid to the other of said spaces causes relative displacement between the cylinder and piston.

2. A drop hammer according to claim 1 wherein the conduit means are disposed internally of the ram and pass through the piston.

3. A drop hammer according to claim 1 wherein an upper end of the ram cylinder is secured to the carrier and a piston rod is attached to the ram piston to project downwardly from the cylinder, a hammer weight being secured to the piston rod and guide means being provided on the carrier for said weight.

4. A drop hammer according to claim 1 wherein the valve means comprises a displaceable member arranged to be exposed at opposite sides to the fluid pressure in said one space of the cylinder and to atmospheric pressure respectively.

5. A drop hammer according to claim 4 wherein resilient means act upon the displaceable valve member to bias it to a position in which the conduit means interconnects said cylinder spaces.

6. A drop hammer according to claim 4 wherein an axial bore is provided in the ram piston in which the displaceable valve member is slidable, said member comprising an outer cylindrical portion sealingly fitting said bore and respective openings being provided in said bore and said cylindrical portion to be mutually registerable to interconnect said cylinder spaces.

7. A drop hammer according to claim 1 wherein a hammer weight is mounted on the carrier to be displaceable by the ram, connection means being provided between the weight and the ram and arranged to permit a limited relative movement therebetween in the direction of ram movement, damping means being provided on the ram to reduce the relative speed between the cylinder and piston at the end of a downwards hammer stroke.

8. A drop hammer according to claim 1 further comprising switching means for automatic cycling operation of the fluid pressure mechanism.

9. A drop hammer comprising, in combination,

a carrier;

a fluid pressure operating mechanism including a ram having a cylinder and piston assembly mounted on said carrier in an upwardly extending position, said piston dividing the cylinder interior into discrete spaces on opposite sides of the piston;

a conduit means arranged to interconnect said cylinder internal spaces, the conduit means being provided with valve means to isolate said spaces from each other, said valve means being displaceable by an increase of pressure in one of said spaces thereby causing a pressure force in that one space, which force displaces said valve means so as to shut off the flow between the spaces, whereby admission of pressure fluid to the other of said spaces causes relative displacement between the cylinder and piston;

a hammer weight mounted on the carrier and displaceable by the ram;

connection means disposed between the weight and the ram, said connection means being arranged to permit a limited relative movement between the weight and the ram in the direction of the ram movement; and

damping means being provided on the ram to reduce the relative speed between the cylinder and the piston at the end of a downwards stroke, said damping means comprising an insertion element and a receiving space that contains the ram fluid, said element and receiving space being disposed on the ram piston and cylinder, or parts moving with said piston and cylinder, respectively, the element being arranged to enter the receiving space during the final part of the hammer stroke, exit of the fluid from the receiving space being restricted while the volume of the space is being reduced by the entry of the element thereinto, whereby an increased resistance is offered to relative movement between the piston and cylinder during the final art of the stroke. 10. A drop hammer accor ing to claim 9 wherein means are provided to adjust the restriction offered to the exit of the fluid from said space during the final part of said downwards stroke. 

1. A drop hammer comprising, in combination, a carrier, a fluid pressure operating mechanism comprising a ram having a cylinder and piston assembly mounted on said carrier in an upwardly extending position, said piston dividing the cylinder interior into discrete spaces on opposite sides of the piston, conduit means arranged to interconnect said cylinder internal spaces, the conduit means being provided with valve means to isolate said spaces from each other, said valve means being displaceable by an increase of pressure in one of said spaces thereby causing a pressure force in that one space, which force displaces said valve means so as to shut off the flow between the spaces whereby admission of pressure fluid to the other of said spaces causes relative displacement between the cylinder and piston.
 2. A drop hammer according to claim 1 wherein the conduit means are disposed internally of the ram and pass through the piston.
 3. A drop hammer according to claim 1 wherein an upper end of the ram cylinder is secured to the carrier and a piston rod is attached to the ram piston to project downwardly from the cylinder, a hammer weight being secured to the piston rod and guide means being provided on the carrier for said weight.
 4. A drop hammer according to claim 1 wherein the valve means comprises a displaceable member arranged to be exposed at opposite sides to the fluid pressure in said one space of the cylinder and to atmospheric pressure respectively.
 5. A drop hammer according to claim 4 wherein resilient means act upon the displaceable valve member to bias it to a position in which the conduit means interconnects said cylinder spaces.
 6. A drop hammer according to claim 4 wherein an axial bore is provided in the ram piston in which the displaceable valve member is slidable, said member comprising an outer cylindrical portion sealingly fitting said bore and respective openings being provided in said bore and said cylindrical portion to be mutually registerable to interconnect said cylinder spaces.
 7. A drop hammer according to claim 1 wherein a hammer weight is mounted on the carrier to be displaceable by the ram, connection means being provided between the weight and the ram and arranged to permit a limited relative movement therebetween in the direction of ram movement, damping means being provided on the ram to reduce the relative speed between the cylinder and piston at the end of a downwards hammer stroke.
 8. A drop hammer according to claim 1 further comprising switching means for automatic cycling operation of the fluid pressure mechanism.
 9. A drop hammer comprising, in combination, A carrier; a fluid pressure operating mechanism including a ram having a cylinder and piston assembly mounted on said carrier in an upwardly extending position, said piston dividing the cylinder interior into discrete spaces on opposite sides of the piston; a conduit means arranged to interconnect said cylinder internal spaces, the conduit means being provided with valve means to isolate said spaces from each other, said valve means being displaceable by an increase of pressure in one of said spaces thereby causing a pressure force in that one space, which force displaces said valve means so as to shut off the flow between the spaces, whereby admission of pressure fluid to the other of said spaces causes relative displacement between the cylinder and piston; a hammer weight mounted on the carrier and displaceable by the ram; connection means disposed between the weight and the ram, said connection means being arranged to permit a limited relative movement between the weight and the ram in the direction of the ram movement; and damping means being provided on the ram to reduce the relative speed between the cylinder and the piston at the end of a downwards stroke, said damping means comprising an insertion element and a receiving space that contains the ram fluid, said element and receiving space being disposed on the ram piston and cylinder, or parts moving with said piston and cylinder, respectively, the element being arranged to enter the receiving space during the final part of the hammer stroke, exit of the fluid from the receiving space being restricted while the volume of the space is being reduced by the entry of the element thereinto, whereby an increased resistance is offered to relative movement between the piston and cylinder during the final part of the stroke.
 10. A drop hammer according to claim 9 wherein means are provided to adjust the restriction offered to the exit of the fluid from said space during the final part of said downwards stroke. 